1. Field of the Invention
Aspects of the present invention relate to a power conditioner for supplying controlled power generated from a fuel cell, a solar battery, or the like to a load, and a method of operating the power conditioner.
2. Description of the Related Art
Power generated from a fuel cell 10 is supplied to a load 40 through a power conditioner as illustrated in FIG. 1. FIG. 1 is specifically a diagram illustrating the structure of a power conditioner disclosed in U.S. Patent Publication No. 2004/0219399. A DC voltage in the range of about 40 V-50 V generated in the fuel cell 10, which is a power source, is raised to a DC voltage in the range of about 360 V-400 V in a main converter 20. The fuel cell 10 includes a plurality of stacked unit cells. Thus, the power outputs generated in each unit cell are added, such that the output voltage of the fuel cell 10 is in the range of 40 V-50 V DC. The DC voltage is raised in the main converter 20, is converted to an AC voltage in an inverter 30, and is supplied to the load 40.
At this point, between the main converter 20 and the inverter 30, power corresponding to a DC voltage is reduced to about 20 V-30 V through an auxiliary converter 60 and is used to operate various components (such as a blower, a motor, a cooling fan, and a controller) that are incorporated into the stack of the fuel cell 10, and to operate controllers such as the main converter 20 and the inverter 30. That is, a part of the power that had been raised to a predetermined voltage in the main converter 20 is diverted to the auxiliary converter 60, reduced to an appropriate voltage, and is then supplied to the various components and controllers. Of course, the output voltage of the auxiliary converter 60 is also supplied to a controller of the auxiliary converter 60. The elements of a system that uses a part of the power generated in the fuel cell 10, for example, the controller that controls the main converter 20, the inverter 30, the auxiliary converter 60, etc., and the various components included in the stack of the fuel cell 10 are generally referred to as balance of plant (BOP) elements. In FIG. 1, the elements are shown as a single BOP elements 70. A storage battery 50 is also used as a power source when power is not adequately supplied to the auxiliary converter 60, such as in the initial start mode of the fuel cell 10. The storage battery 50 is charged by the output voltage of the main converter 20 while the fuel cell 10 operates normally. The charged storage battery 50 is used as the power source of the auxiliary converter 60 in the initial start mode.
However, in the architecture illustrated in FIG. 1, the voltage supplied to the BOP elements 70 must pass through both the main converter 20 and the auxiliary converter 60, and accordingly an unavoidable power loss occurs at two points during the voltage conversion process. That is, power loss occurs when part of the power is changed into heat during the voltage conversion (i.e., increase) process in the main converter 20 and then again during the reverse conversion (i.e., decrease) in the auxiliary converter 60. As a result, power supplied to the BOP elements 70 after passing through the converters 20 and 60 is the power remaining after the power output from the fuel cell 10 has been greatly reduced. To lessen the loss of power, a part of the power supplied from the fuel cell 10 could be directly supplied to the BOP elements 70 without passing through the converters 20 and 60. However, since the output voltage of the fuel cell 10 varies as a function of the operating conditions of the load 40, the output voltage of the fuel cell 10 also varies considerably. Accordingly, it is not possible to use this bypass system when power is directly supplied to the BOP elements 70 because the operating conditions of the entire system become unstable.
Therefore, in order to solve these and/or other problems, there is a need to develop an apparatus and method that avoids the power loss by decreasing the number of times of voltage conversions while supplying stable power to BOP elements 70.